WO2022179612A1

WO2022179612A1 - Multi-mode combined short-circuit protection circuit, and working method and use thereof

Info

Publication number: WO2022179612A1
Application number: PCT/CN2022/077963
Authority: WO
Inventors: 王鲁; 曹鹏辉; 张小峰; 付翀丽; 王英武; 王俊峰
Original assignee: 西安微电子技术研究所
Priority date: 2021-02-26
Filing date: 2022-02-25
Publication date: 2022-09-01
Also published as: CN112994430A; CN112994430B

Abstract

The present invention relates to the technical field of short-circuit protection circuits. Disclosed are a multi-mode combined short-circuit protection circuit, and a working method therefor. The multi-mode combined short-circuit protection circuit specifically comprises a sampling circuit, a constant-current protection circuit, a hiccup protection circuit, a reference voltage circuit and a voltage division circuit; the constant-current protection circuit comprises an operational amplifier U1A, and the hiccup protection circuit comprises an operational amplifier U1B, when an output of a switch power supply is short-circuited, constant-current protection is performed first, and then hiccup protection is performed, and the hiccup protection mode can be started when a set constant-current protection time is reached; if a short-circuit fault persists, a protection circuit repeats a working mode, "constant-current protection-hiccup protection"; and when the short circuit fault of the switching power supply is eliminated, and the normal function is restored. The short-circuit protection circuit not only has the feature of high external load capacitance of constant-current protection, but also has the feature of low short-circuit power consumption of hiccup protection, and also ensures that hiccup protection can be entered when the constant-current protection reaches the designed time, thereby solving the problem of high short-circuit power consumption of a high-power switch power supply, and also having the advantage of high external load capacitance.

Description

A multi-mode combined short-circuit protection circuit and its working method and application

technical field

The invention belongs to the technical field of short-circuit protection circuits, and in particular relates to a multi-mode combined short-circuit protection circuit and its working method and application.

Background technique

The switching power supply continues to develop in the direction of high power, small size, high efficiency, and high reliability. With the advancement of high-efficiency technology, the power dissipation of the switching power supply has been effectively controlled, the volume size has been continuously reduced, and the power density has become higher and higher. There are two kinds of short-circuit protection circuits commonly used at present, one is a constant current protection circuit, and the other is a hiccup protection circuit.

(1) Constant current protection circuit

Constant current protection is an accurate power control method, the protection circuit is shown in Figure 1. Generally, a sampling resistor or a current transformer is used to detect the change of the current, and the current sampling signal is converted into a voltage sampling signal, which is compared with the reference level differentially. The differential signal controls the output level through the op amp proportional and integral, and then controls the level of the feedback signal. The feedback signal is transmitted in isolation or directly triggers the COM terminal level of the pulse width controller, thereby controlling the size of the output duty cycle, and finally realizing the precise control of the output power.

When the output terminal of the switching power supply is short-circuited, the current increases rapidly to trigger the constant current protection, and the output duty cycle of the pulse width controller is limited, which greatly reduces the output power and achieves the purpose of reducing short-circuit power consumption. In addition, when the output terminal of the switching power supply is connected to a large capacitive load for power-on, the constant current protection will limit the sudden change of the duty cycle of the pulse width control, and continuously change from small to large until the output voltage is established. The advantage of strong sexual load capacity. However, as the output power of the switching power supply continues to increase, the current during short-circuit protection also increases, resulting in a continuous increase in short-circuit power consumption and limiting the scope of application of constant-current protection.

(2) Hiccup protection circuit

Hiccup protection is a pulse power control method, the protection circuit is shown in Figure 2. Generally, a sampling resistor or a current transformer is used to detect the change of the input current, convert the current sampling signal into a voltage sampling signal, compare it with the reference level, control the output level of the comparator, and then control the level of the feedback signal. The feedback signal directly triggers the COM terminal level of the pulse width controller, thereby controlling the change of the output duty cycle. The duty cycle changes from large to 0, and finally realizes the pulse control of the output power.

When the output terminal of the switching power supply is short-circuited, the input current increases rapidly to trigger the output of the comparator to flip, and the output duty cycle of the pulse width controller increases from 0 to 0, and no energy is output; increasing the hiccup protection time can greatly reduce the power consumption of the short-circuit protection. . However, when the switching power supply is short-circuited, during the collection of the pulse power signal, the pulse width controls the output maximum duty cycle, the transformer is difficult to reset, and there is a saturation problem. There is a risk of burnout, so the pulse power time must be set very short. When the output terminal of the switching power supply is powered on with a large capacitive load, the input current increases rapidly, and the short pulse power time often cannot provide enough energy for the output load, and the hiccup protection is triggered, resulting in the output voltage of the switching power supply cannot be The establishment has certain limitations.

technical problem

The purpose of the present invention is to provide a multi-mode combined short-circuit protection circuit and its working method and application, which solve the problem of large short-circuit power consumption of high-power switching power supplies, and have the advantages of strong capacitive load capacity.

technical solutions

The present invention is achieved through the following technical solutions:

A multi-mode combined short-circuit protection circuit includes a sampling circuit, a constant current protection circuit, a hiccup protection circuit, a reference reference voltage circuit and a voltage divider circuit; the constant current protection circuit includes an operational amplifier U1A, the hiccup protection circuit includes an operational amplifier U1B, and the operational amplifier U1B; Put the reverse input terminal of U1A and connect it with the sampling circuit;

The reference voltage circuit includes resistor R6, resistor R7, resistor R8 and Zener tube Z1; one end of resistor R8 is connected to the power supply terminal, the other end is connected to resistor R6 and the cathode of Zener tube Z1, and the other end of resistor R6 is connected to the positive input of the operational amplifier U1A terminal, the forward input terminal of the operational amplifier U2A and one end of the resistor R7; the anode of the Zener tube Z1 and the other end of the resistor R7 are grounded;

The voltage divider circuit includes resistor R10, resistor R11, resistor R12, voltage regulator Z2, capacitor C4 and transistor Q1; one end of resistor R10 is connected to the output end of U1A, the cathode of diode D3 and one end of capacitor C2, and the other end of resistor R10 is connected to voltage regulator The cathode of the tube Z2; the anode of the zener tube Z2 is connected to one end of the resistor R11 and the base b of the transistor Q1; the collector c of the transistor Q1 is connected to one end of the resistor R12, one end of the capacitor C4 and the forward input end of the operational amplifier U1B; The other end of the resistor R12 is connected to the power supply end; the other end of the resistor R11 and the emitter e of the transistor Q1 are grounded.

Further, the constant current protection circuit also includes a resistor R15, a diode D3, a capacitor C2 and a resistor R9; one end of the resistor R9 is connected to the reverse input end of the operational amplifier U1A, and the other end of the resistor R9 is connected to the other end of the capacitor C2; the anode of the diode D3 is connected to the resistor One end of R15 and the feedback signal end; the other end of the resistor R15 is connected to the power supply end.

Further, the hiccup protection circuit also includes a MOS tube M1, a resistor R13, a resistor R14, a capacitor C3 and a diode D4; the drain D of the MOS tube M1 is connected to the anode of the diode D3, one end of the resistor R15 and the feedback signal terminal, and the gate of the MOS tube M1 The pole G is connected to one end of the resistor R14, one end of the capacitor C3 and one end of the resistor R13; the other end of the resistor R13 is connected to the cathode of the diode D4; the anode of the diode D4 is connected to the output port of the operational amplifier U1B; the source of the MOS tube M1, the other end of the resistor R14 and the capacitor C3 The other end is grounded.

Further, the sampling circuit includes a current transformer L1, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a diode D1, a diode D2 and a capacitor C1; one end of the current transformer L1 is grounded, and the other end is connected to one end of the resistor R1, a diode The anode of D1 and the anode of diode D2, the other end of resistor R1 is grounded; the cathode of diode D1 is connected to one end of resistor R2, and the other end of resistor R2 is grounded; the cathode of diode D2 is connected to one end of resistor R3, and the other end of resistor R3 is connected to capacitor C1 One end of the resistor R4, one end of the resistor R5, the other end of the capacitor C1 and the other end of the resistor R4 are grounded, and the other end of the resistor R5 is connected to the reverse input end of the operational amplifier U1A.

Furthermore, the resistance R13 is 10Ω-20Ω, and the resistance R14 is 1MΩ-2MΩ.

Further, the resistance R3 is 90Ω to 110Ω.

Further, the resistance R4 is 9kΩ to 11kΩ.

The invention also discloses a working method of the multi-mode combined short-circuit protection circuit when the switching power supply works normally, including the following processes:

The voltage of the inverting input terminal of the operational amplifier U1A is lower than the reference voltage of the non-inverting input terminal, the output terminal is high level, and the diode D3 is reversely cut off, which does not affect the feedback signal at the feedback signal terminal;

The high level of the output terminal passes through the current limiting resistor R10, the resistor R11 and the be junction of the transistor Q1, and supplies power to the Zener tube Z2 to ensure the normal operation of the Zener tube Z2; the collector of the transistor Q1 is powered by the power supply terminal through the pull-up resistor R12. Q1 is in a saturated conduction state, the collector of transistor Q1 is low level; the level of the non-inverting input terminal of the operational amplifier U1B is lower than the reference voltage of the inverting input terminal, the output terminal of the operational amplifier U1B is low level, and the MOS tube cannot be turned on. M1, does not affect the feedback signal at the feedback signal port.

The invention also discloses a working method of the multi-mode combined short-circuit protection circuit when the output of the switching power supply is short-circuited, including the following processes:

The sampling voltage of the inverting input terminal of the op amp U1A rises, and compared with the reference voltage of the non-inverting input terminal, the generated differential voltage is adjusted by the proportional resistor R9 and the integrating capacitor C2. The output terminal of the op amp U1A drops to a low level; the diode D3 is positive Turn on, pull down the feedback signal at the feedback signal terminal, the feedback signal is positively correlated with the output duty cycle of the pulse width control, and the output duty cycle of the pulse width control is limited; the output end of the op amp U1A is low level, the voltage regulator tube Z2 is in the cut-off state; the transistor Q1 does not work, the voltage of the power supply terminal passes through the resistor R12 to charge the capacitor C4, the charging time of the capacitor C4 is the constant current protection time, and the switching power supply is in the constant current protection mode;

The voltage of the non-inverting input terminal of the op amp U1B is higher than the reference voltage of the inverting input terminal, the output terminal of the op amp U1B is turned to a high level, and the forward voltage drops through the diode D4, and the current limiting resistor R13 charges the capacitor C3 and rises to MOS After the gate threshold voltage of tube M1, the MOS tube is turned on, the drain and source are turned on, the feedback signal at the feedback signal terminal is pulled down from low level to 0, the pulse width control output is turned off, and the switching power supply has no energy output; this When the sampling voltage of the inverting input terminal of the operational amplifier U1A drops rapidly, the voltage regulator Z2 is turned on, the output terminal of the operational amplifier U1B is turned to a low level, and the capacitor C3 starts to discharge through the resistor R14, and it drops to the gate threshold voltage of the MOS tube M1. Before, the MOS tube M1 was in the conducting state, and the switching power supply was in the hiccup protection mode;

If the short-circuit fault persists, the sampling voltage of the inverting input terminal of the operational amplifier U1A rises again, and the above working process is repeated.

The invention also discloses a high-power switching power supply, which includes the multi-mode combined short-circuit protection circuit.

beneficial effect

Compared with the prior art, the present invention has the following beneficial technical effects:

The invention designs a short-circuit protection circuit for high-power switching power supply, including a sampling circuit, a constant current protection circuit, a hiccup protection circuit, a reference reference voltage circuit and a voltage divider circuit; the constant current protection circuit includes an operational amplifier U1A, a hiccup protection circuit Including the operational amplifier U1B, it not only has the characteristics of strong constant current protection of capacitive load, but also has the characteristics of hiccup protection and low power consumption. The sampling line uses a current transformer to sample the input current, with low loss, the current signal is converted into a relatively stable DC level, is less affected by the input voltage, and has a small temperature drift, which is mainly related to the output load current, which is conducive to protection design; this line uses current The transformer collects the input current and converts the current signal into a voltage signal; dual operational amplifiers are used for signal processing, and one of the operational amplifiers is used as a proportional integral to perform constant current protection control, adjust the constant current time, and ensure a large capacitive switching power supply. Load capacity; another op amp is used as a comparator to perform hiccup protection control, adjust the hiccup time, and greatly reduce short-circuit power consumption.

Further, the sampling circuit of the present invention uses two diodes, and the sampling signal is processed as a DC level, which is mainly related to the output load current, and the constant current protection point is stable, which is suitable for switching power supplies with a wide range of input voltages.

Further, the resistance of the resistor R3 is small, the charging time of the capacitor C1 is generally shorter than one switching power supply cycle, the resistance of the resistor R4 is large, and the discharging time of the capacitor C1 is generally longer than 100 switching power supply cycles, thus ensuring the sampling voltage. of stability.

The invention also discloses a working method of a multi-mode combined short-circuit protection circuit when the output of the switching power supply is short-circuited. The hiccup protection mode can be turned on; the short-circuit fault persists, and the protection circuit repeats the "constant current protection-hiccup protection" working mode; the short-circuit fault of the switching power supply is eliminated and the normal function is restored. Through the design of the voltage divider circuit, it is ensured that the constant current protection is carried out first, and then the hiccup protection is carried out. At the same time, it is also ensured that the hiccup protection can be entered when the constant current protection reaches the design time, which not only solves the problem of large short-circuit power consumption of high-power switching power supplies, It also has the advantage of strong capacitive load capacity.

The multi-mode combined short-circuit protection circuit of the present invention is applied in high-power switching power supplies, not only solves the problem of high power consumption of constant current protection, but also solves the problem of weak capability of hiccup protection for capacitive loads, and also avoids internal devices from overheating. Risk of electrical stress.

Description of drawings

Fig. 1 is the connection schematic diagram of the traditional constant current protection circuit;

Figure 2 is a schematic diagram of the connection of a traditional hiccup protection circuit;

3 is a schematic diagram of the connection of the short-circuit protection circuit of the multi-mode combination of the present invention;

4 is a voltage waveform diagram of a key node of a multi-mode combined short-circuit protection line of the present invention;

Figure 5 is a schematic diagram of the circuit connection of the constant current protection circuit applied to the switching power supply;

Figure 6 is a schematic diagram of the circuit connection of the hiccup protection circuit applied to the switching power supply;

7 is a schematic diagram of the circuit connection of the multi-mode combined short-circuit protection circuit of the present invention applied to a switching power supply;

FIG. 8 is a measured waveform diagram of the voltage of the key nodes of the short-circuit protection line of the multi-mode combination of the present invention;

Fig. 9 is the measured waveform diagram of the output current of the short-circuit protection line of the multi-mode combination of the present invention;

FIG. 10 is a waveform diagram of the output voltage startup with a full load of 2000 μF for the multi-mode combined short-circuit protection circuit of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be further described in detail below in conjunction with specific embodiments, which are to explain rather than limit the present invention.

As shown in FIG. 3, the present invention discloses a multi-mode combined short-circuit protection circuit, including a sampling circuit, a constant current protection circuit, a hiccup protection circuit, a reference reference voltage circuit and a voltage divider circuit; the sampling circuit includes a current transformer L1, Resistor R1, resistor R2, resistor R3, resistor R4, resistor R5, diode D1, diode D2 and capacitor C1; the reference reference voltage circuit includes resistor R6, resistor R7, resistor R8 and Zener tube Z1; the voltage divider circuit includes resistor R10, Resistor R11, resistor R12, voltage regulator Z2, capacitor C4 and transistor Q1; constant current protection circuit includes op amp U1A, resistor R15, diode D3, capacitor C2 and resistor R9; hiccup protection circuit includes op amp U1B, MOS tube M1, Resistor R13, resistor R14, capacitor C3 and diode D4.

One end of the current transformer L1 is grounded, and the other end is connected to one end of the resistor R1, the anode of the diode D1 and the anode of the diode D2. The other end of resistor R1 is connected to ground. The cathode of the diode D1 is connected to one end of the resistor R2, and the other end of the resistor R2 is grounded. The cathode of diode D2 is connected to one end of resistor R2. The other end of the resistor R2 is connected to one end of the capacitor C1, one end of the resistor R4 and one end of the resistor R5. The other end of the capacitor C1 is grounded, and the other end of the resistor R4 is grounded. The other end of the resistor R5 is connected to one end of the resistor R9 and the inverting input end of the operational amplifier U1A.

The other end of the resistor R9 is connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to the output end of the operational amplifier U1A, the cathode of the diode D3, and one end of the resistor R10, and the other end of the resistor R10 is connected to the cathode of the Zener tube Z2. Port 01 is connected to one end of the resistor R8, one end of the resistor R12, one end of the resistor R15, and the 8 end of the forward power supply port of the operational amplifier U1A. The other end of the resistor R8 is connected to one end of the resistor R6 and the cathode of the zener tube Z1. The anode of the Zener tube Z1 is grounded. The other end of the resistor R6 is connected to one end of the resistor R7, the non-inverting input port 3 of the operational amplifier U1A and the inverting input port 6 of the U1B, and the other end of the resistor R7 is grounded. The anode of the voltage regulator Z2 is connected to one end of the resistor R11 and the base b of the transistor Q1. The other end of resistor R11 is connected to ground. The emitter e of the transistor Q1 is grounded. The collector c of the transistor Q1 is connected to the other end of the resistor R12, one end of the capacitor C4 and the non-inverting input port 5 of U1B. The other end of capacitor C4 is grounded. The negative power supply port of the operational amplifier U1B is grounded. The output port 7 of the operational amplifier U1B is connected to the anode of the diode D4, the cathode of the diode D4 is connected to one end of the resistor R13, the other end of the resistor R13 is connected to one end of the capacitor C3, one end of the resistor R14, and the gate G of the MOS transistor M1. The other end of capacitor C3 is grounded. The other end of resistor R14 is grounded. The source S of the MOS transistor M1 is grounded. The drain D of the MOS transistor M1 is connected to the anode of the diode D13, the other end of the resistor R15 and the port 02. Port 01 is connected to the supply voltage, and port 02 is connected to the feedback signal.

The current transformer L1 detects the input current I _IN , and the sampling current is 1/N of I _IN . After being rectified by the diode D1, it flows through the sampling resistor R2 to form the sampling voltage R2*I _IN /N. Resistor R1 provides a reset loop for the current transformer. The cathode of diode D2 is equal to the cathode of diode D1, the sampling voltage R2*I _IN /N charges the capacitor C1 through the resistor R3, and the resistor R4 discharges the capacitor C1 to form a stable DC voltage, which is reversed through the resistor R5 to the op amp U1A Input port 2 terminal. Port 01 is the power supply terminal, which supplies power to the Zener tube Z1 through the current limiting resistor R8, and is divided by the resistor R6 and the resistor R7 to provide the reference reference voltage.

Figure 4 shows the working waveform of the key node voltage inside the short-circuit protection line. The output load of the switching power supply is short-circuited at time t1, and the protection circuit starts to work. First enter the constant current short-circuit protection mode, the time is t2 ~ t3; after the constant current protection time is over, enter the hiccup protection mode, the time is t3 ~ t4; the short-circuit fault persists, the protection circuit repeats the "constant current protection - hiccup protection" work mode; at t5 time, the short-circuit fault of the switching power supply is eliminated and the normal function is restored.

The working conditions of the short-circuit protection circuit components are described in detail below.

When the switching power supply is working normally, the voltage of the inverting input port 2 of the op amp U1A is lower than the reference voltage of the non-inverting input port 3, the output port 1 of the op amp is high level, the diode D3 is reversely cut off, and will not connect to port 02. The feedback signal at the place has an effect. The high level of the output port 1 of the op amp passes through the current limiting resistor R10, the resistor R11 and the be junction of the transistor Q1 to supply power to the Zener tube Z2 to ensure the normal operation of the Zener tube Z2; the Zener tube Z2, the resistor R10 and the resistor R11 points voltage, to ensure that the base level of the transistor Q1 is higher than 0.7V; the collector c of the transistor Q1 is powered by the port 01 through the pull-up resistor R12, and the resistance value of the resistor R12 is large to ensure that the transistor Q1 is in a saturated conduction state, and the collector c of the transistor Q1 to low level. The op amp U1B is used as a comparator. The voltage of the non-inverting input port 5 of the op amp U1B is lower than the reference voltage of the inverting input port 6. The output port 7 of the op amp U1B is low level, and the MOS tube M1 cannot be turned on. Affects the feedback signal at port 02.

Resistor R12 is 100kΩ～200kΩ, and the charging time of resistor R12 to capacitor C4 is constant current protection time, which is generally about 5 times the startup delay of switching power supply, which ensures the large capacitive load capacity of switching power supply; resistor R14 is 1MΩ～2MΩ, The discharge time of the resistor R14 to the capacitor C3 is the hiccup protection time, which is generally about 10 times of the constant current protection of the switching power supply to ensure a small short-circuit power consumption of the switching power supply; the resistor R13 is a current limiting resistor, generally 10Ω～20Ω, to avoid surge Current damage to components.

When the output of the switching power supply is short-circuited, the sampling voltage of the inverting input port 2 of the op amp U1A rises rapidly. Compared with the reference voltage of the non-inverting input port 3, the generated differential voltage is proportionally amplified by the resistor R9 of the op amp U1A and integrated by the capacitor C2. function, adjust the level of the output port 1 of the op amp U1A to drop to a low level; the diode D3 is forward-conducting, pulling down the feedback signal at port 2, the feedback signal is positively related to the output duty cycle of the pulse width control, so the pulse width The duty cycle of the control output is limited; the output port 1 of the op amp U1A is at a low level, which cannot reach the voltage regulation value of the Zener tube Z2, and the Zener tube Z2 is in the cut-off state; the transistor Q1 does not work, and the voltage of the port 01 passes through The resistor R12 charges the capacitor C4, the charging time of the capacitor C4 is the constant current protection time, and the switching power supply is in the constant current protection mode. The voltage of the non-inverting input port 5 of the op amp U1B is higher than the reference voltage of the inverting input port 6, and the output port 7 of the op amp U1B is turned to a high level. The forward voltage drops through the diode D4, and the current-limiting small resistor R13 is The capacitor C3 is charged and reaches the gate threshold voltage of the MOS tube M1, the MOS tube is turned on, the drain-source is turned on, the feedback signal at port 02 is pulled down from low level to 0, the pulse width control output is turned off, and the switching power supply has no energy output. , the power consumption is very small; at this time, the sampling voltage drops rapidly, the voltage regulator Z2 is turned on, the output terminal of the op amp U1B is turned to a low level, and the capacitor C3 starts to discharge slowly through the resistor R14, which is set to a larger resistor. , so that the MOS tube M1 is in the conduction state for a long time, which greatly reduces the short-circuit power consumption, and the switching power supply is in the hiccup protection mode. The short-circuit fault persists, and the sampling voltage of the inverting input port 2 of the operational amplifier U1A rises rapidly again, and the above working process is repeated.

The circuit of the constant current protection method applied to the switching power supply is shown in Figure 5. It is generally used to adjust the feedback signal of the latter stage of the switching power supply, and the output duty cycle of the pulse width controller is controlled by the isolated feedback. There are many applications in the power supply.

The circuit of the hiccup protection method applied to the switching power supply is shown in Figure 6. It is generally used to adjust the front-end feedback signal of the switching power supply and directly control the output duty cycle of the pulse width controller, which is widely used.

The circuit of the multi-mode combined short-circuit protection circuit protection method of the present invention applied to the switching power supply is shown in FIG. 7 . The current transformer is used for signal sampling. The diode D1 and the diode D2 have the functions of suppressing temperature drift and preventing current inversion; the resistor R3 is designed to be 90Ω～110Ω, the resistance value of the resistor R3 is small, and the charging time of the capacitor C1 is generally shorter than 1 In the switching power supply cycle, the resistor R4 is designed to be 9kΩ～11kΩ, and the resistance value of the resistor R4 is relatively large. The discharge time of the capacitor C1 is generally longer than 100 switching power supply cycles, thus ensuring the stability of the sampling voltage; the output of the op amp U1A, from high power There is a certain delay in the transition from flat to low level. The use of the voltage regulator Z2 makes the base b of the transistor Q1 get a certain level (high level or low level), and the transistor Q1 works at a certain level. mode (off state or saturated conduction state); VCC2 charges capacitor C4 through resistor R12, and the voltage on capacitor C4 is the time when the voltage of the non-inverting input port 5 of the op amp U1B reaches the reference voltage of the inverting input port 6, which is Constant current protection time; the voltage of VCC2 is higher than the reference voltage and reaches the designed constant current time, the level of the output port 7 of the op amp U1B is normally reversed, and the capacitor C3 gets a high enough voltage, which is higher than the threshold voltage of the MOS tube M1, The MOS tube is turned on and turned on; the diode D4 plays the role of forward charging and reverse current cut-off, the charge of the capacitor C3 is slowly discharged through the resistor R14, and the time when the voltage on the capacitor C3 decreases to the threshold voltage of the MOS tube is the hiccup time.

The sampling signal of the short-circuit protection circuit of the present invention is stable, mainly related to the output load current; the short-circuit protection working sequence is determined, and the constant current protection is performed first, and then the hiccup protection is performed; and the hiccup protection mode can be turned on when the set constant current protection time is reached. Applied in high-power switching power supply, it not only solves the problem of high power consumption of constant current protection, but also solves the problem of weak capability of hiccup protection of capacitive load, and also avoids the risk of over-stress of internal devices.

Apply it to the DC/DC converter, the working frequency is 500kHz, the input voltage is 28V, the output voltage is 5V, the output current is 20A, and the output power is 100W. The circuit is shown in Figure 7. The current transformer samples the input current, the port 01 is connected to the power supply VCC2 of the rear stage, and the port 02 is connected to the feedback signal. When the output load of the DC/DC converter is short-circuited, the measured waveform of the short-circuit protection line key node voltage is shown in Figure 8, the output load current waveform is shown in Figure 9, and the output voltage startup waveform with a 2000μF capacitive load is shown in Figure 10.

As shown in Figure 8, channel 1 is the voltage waveform of the inverting input port 2 of the op amp U1A, channel 2 is the voltage waveform of the non-inverting input port 5 of the op amp U1B, and channel 3 is the gate voltage waveform of the MOS transistor M1. Channel 4 is the drain voltage waveform of the MOS transistor M1.

As shown in Figure 9, channel 1 is the voltage waveform of the inverting input port 2 of the op amp U1A, and channel 4 is the output current waveform when the output load is short-circuited.

As shown in Figure 10, channel 1 is the DC/DC converter when the input voltage is 28V, the output current is 20A, and the capacitive load is 2000μF, the output voltage startup waveform.

As shown in Figure 8 and Figure 9, the actual test waveform is basically consistent with the theoretical analysis waveform in Figure 4. The constant current protection time is about 15ms, the hiccup protection time is about 150ms, and the average short-circuit power consumption is about 5W; as shown in Figure 10, it is the startup waveform with a 2000μF capacitive load, there is no startup overshoot, and the startup delay is about 2.5ms. The new short-circuit protection circuit has been applied to the design of military DC/DC series converters with a bus input of 20V to 50V and an output power of 100W.

The effect of the present invention is verified through experiments. Apply it to the DC/DC converter, the working frequency is 500kHz, the input voltage is 28V, the output voltage is 5V, and the output current is 20A. When the constant current protection circuit is used, as shown in Figure 5, the short-circuit power consumption is about 30W and the capacitive load capacity is 2000μF; when the hiccup protection circuit is used, as shown in Figure 6, the short-circuit power consumption is about 5W and the capacitive load capacity is 300μF. Using the short-circuit protection scheme of the present invention, as shown in FIG. 7 , the short-circuit power consumption is about 5W, the capacitive load capacity is 2000 μF, the capacitive load capacity is strong, and the short-circuit power consumption is significantly reduced.

Claims

A multi-mode combined short-circuit protection circuit is characterized in that it includes a sampling circuit, a constant current protection circuit, a hiccup protection circuit, a reference reference voltage circuit and a voltage divider circuit; the constant current protection circuit includes an operational amplifier U1A, and the hiccup protection circuit includes an operational amplifier. Put U1B, the inverting input terminal of op amp U1A is connected to the sampling circuit;

The reference voltage circuit includes resistor R6, resistor R7, resistor R8 and Zener tube Z1; one end of resistor R8 is connected to the power supply terminal, the other end is connected to resistor R6 and the cathode of Zener tube Z1, and the other end of resistor R6 is connected to the positive input of the operational amplifier U1A terminal, the forward input terminal of the operational amplifier U2A and one end of the resistor R7; the anode of the Zener tube Z1 and the other end of the resistor R7 are grounded;

The voltage divider circuit includes resistor R10, resistor R11, resistor R12, voltage regulator Z2, capacitor C4 and transistor Q1; one end of resistor R10 is connected to the output end of U1A, the cathode of diode D3 and one end of capacitor C2, and the other end of resistor R10 is connected to voltage regulator The cathode of the tube Z2; the anode of the zener tube Z2 is connected to one end of the resistor R11 and the base b of the transistor Q1; the collector c of the transistor Q1 is connected to one end of the resistor R12, one end of the capacitor C4 and the forward input end of the operational amplifier U1B; The other end of the resistor R12 is connected to the power supply end; the other end of the resistor R11 and the emitter e of the transistor Q1 are grounded.
A multi-mode combined short-circuit protection circuit according to claim 1, wherein the constant current protection circuit further comprises a resistor R15, a diode D3, a capacitor C2 and a resistor R9; one end of the resistor R9 is connected to the reverse input terminal of the operational amplifier U1A , the other end of the resistor R9 is connected to the other end of the capacitor C2; the anode of the diode D3 is connected to one end of the resistor R15 and the feedback signal end; the other end of the resistor R15 is connected to the power supply end.
The multi-mode combined short-circuit protection circuit of claim 1, wherein the hiccup protection circuit further comprises a MOS tube M1, a resistor R13, a resistor R14, a capacitor C3 and a diode D4; the drain D of the MOS tube M1 is connected to the diode The anode of D3, one end of the resistor R15 and the feedback signal end, the gate G of the MOS tube M1 is connected to one end of the resistor R14, one end of the capacitor C3 and one end of the resistor R13; the other end of the resistor R13 is connected to the cathode of the diode D4; the anode of the diode D4 is connected to the op amp U1B The output port is connected; the source of the MOS tube M1, the other end of the resistor R14 and the other end of the capacitor C3 are grounded.
The multi-mode combined short-circuit protection circuit of claim 1, wherein the sampling circuit comprises a current transformer L1, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a resistor R5, a diode D1, a diode D2 and a capacitor C1; one end of current transformer L1 is grounded, the other end is connected to one end of resistor R1, the anode of diode D1 and the anode of diode D2, the other end of resistor R1 is grounded; the cathode of diode D1 is connected to one end of resistor R2, and the other end of resistor R2 is grounded; The cathode of diode D2 is connected to one end of resistor R3, the other end of resistor R3 is connected to one end of capacitor C1, one end of resistor R4 and one end of resistor R5, the other end of capacitor C1 and the other end of resistor R4 are grounded, and the other end of resistor R5 Connect to the inverting input of the op amp U1A.
The multi-mode combined short-circuit protection circuit according to claim 4, wherein the resistance R13 is 10Ω-20Ω, and the resistance R14 is 1MΩ-2MΩ.
The multi-mode combined short-circuit protection circuit of claim 1, wherein the resistance R3 is 90Ω～110Ω.
The multi-mode combined short-circuit protection circuit of claim 1, wherein the resistor R4 is 9kΩ～11kΩ.
The working method of a multi-mode combined short-circuit protection circuit when the switching power supply works normally according to any one of claims 1 to 7, characterized in that it includes the following process:

The voltage of the inverting input terminal of the operational amplifier U1A is lower than the reference voltage of the non-inverting input terminal, the output terminal is high level, and the diode D3 is reversely cut off, which does not affect the feedback signal at the feedback signal terminal;

The high level of the output terminal passes through the current limiting resistor R10, the resistor R11 and the be junction of the transistor Q1, and supplies power to the Zener tube Z2 to ensure the normal operation of the Zener tube Z2; the collector of the transistor Q1 is powered by the power supply terminal through the pull-up resistor R12. Q1 is in a saturated conduction state, the collector of transistor Q1 is low level; the level of the non-inverting input terminal of the operational amplifier U1B is lower than the reference voltage of the inverting input terminal, the output terminal of the operational amplifier U1B is low level, and the MOS tube cannot be turned on. M1, does not affect the feedback signal at the feedback signal port.
The working method of a multi-mode combined short-circuit protection circuit when the output of the switching power supply is short-circuited according to any one of claims 1 to 7, characterized in that, comprising the following process:

The sampling voltage of the inverting input terminal of the op amp U1A rises, and compared with the reference voltage of the non-inverting input terminal, the generated differential voltage is adjusted by the proportional resistor R9 and the integrating capacitor C2. The output terminal of the op amp U1A drops to a low level; the diode D3 is positive Turn on, pull down the feedback signal at the feedback signal terminal, the feedback signal is positively correlated with the output duty cycle of the pulse width control, and the output duty cycle of the pulse width control is limited; the output end of the op amp U1A is low level, the voltage regulator tube Z2 is in the cut-off state; the transistor Q1 does not work, the voltage of the power supply terminal passes through the resistor R12 to charge the capacitor C4, the charging time of the capacitor C4 is the constant current protection time, and the switching power supply is in the constant current protection mode;

The voltage of the non-inverting input terminal of the op amp U1B is higher than the reference voltage of the inverting input terminal, the output terminal of the op amp U1B is turned to a high level, and the forward voltage drops through the diode D4, and the current limiting resistor R13 charges the capacitor C3 and rises to MOS After the gate threshold voltage of tube M1, the MOS tube is turned on, the drain and source are turned on, the feedback signal at the feedback signal terminal is pulled down from low level to 0, the pulse width control output is turned off, and the switching power supply has no energy output; this When the sampling voltage of the inverting input terminal of the operational amplifier U1A drops rapidly, the voltage regulator Z2 is turned on, the output terminal of the operational amplifier U1B is turned to a low level, and the capacitor C3 starts to discharge through the resistor R14, and it drops to the gate threshold voltage of the MOS tube M1. Before, the MOS tube M1 was in the conducting state, and the switching power supply was in the hiccup protection mode;

If the short-circuit fault persists, the sampling voltage of the inverting input terminal of the operational amplifier U1A rises again, and the above working process is repeated.
A high-power switching power supply, characterized in that it comprises the multi-mode combined short-circuit protection circuit of claims 1 to 7.